All-hydraulic transmissions are known in the prior art. In U.S. Pat. No. 3,199,286 “HYDROSTATIC DRIVE” to Anderson, issued Aug. 10, 1965, a modular hydraulic drive uses a single pump driving separate motors for each of four wheels to provide step-less acceleration. The hydraulic drive includes control valves at each wheel and recharging of low fluids. In U.S. Pat. No. 3,641,765 “HYDROSTATIC VEHICLE TRANSMISSION” to Hancock et al., issued Feb. 15, 1975, the four-wheel hydrostatic drive has special sets of one-way valves and restrictive connections to permit differentiation and provide traction control between the front and rear axles.
There is a need in the art for a transmission that permits a return to the proven but considerably lower speed engines with reduced torque loss in order to increase gasoline engine vehicle efficiency and reduce the weight and cost of manufacture of cars. There is also a need in the art for a transmission that allows a car to change speeds, while the engine operates at a more constant speed. Although the transmissions in current use in most automobiles require the engine to cycle between low speeds and very high speeds during acceleration, an engine is much more fuel-efficient when running at a constant speed.
All-hydraulic transmissions have been used effectively in slow-moving heavy machinery such as tractors and lightweight vehicles such as golf carts and all-terrain vehicles (ATV's). Although all-hydraulic transmissions have been contemplated for automobiles, the inefficiency of hydraulic transmissions in the prior art has made them impractical for use in automobiles. Scaling a hydraulic transmission of the prior art for use in an automobile would produce an unacceptably large, heavy, and noisy transmission, and such transmissions would be larger, heavier, and noisier than the transmissions currently used in automobiles.
Although an internal combustion engine is the industry standard for automobiles in the United States, several major automobile manufacturers are researching a homogeneous-charge-compression-ignition (HCCI) engine. In a conventional gasoline engine, the air-fuel mixture is ignited by a spark plug to create power. In an HCCI engine, similar to in a diesel engine, a piston compresses the air-fuel mixture to increase its temperature until it ignites. It is estimated that an HCCI engine is capable of a 30% increase in fuel economy over a standard gasoline internal combustion engine. However, a major hurdle for implementation of HCCI technology in automobiles is a difficulty in controlling the combustion both at low and at high engine speeds.
There is a need in the art for a transmission, which provides the necessary power to run an automobile while allowing its engine speed to remain in a relatively narrow low-to-moderate range where the combustion in HCCI engines is more easily controlled. Such a transmission allows implementation of more fuel efficient HCCI engines on gasoline-powered vehicles.
Hydraulic pumps and motors are also well known and widely used, having reciprocating pistons mounted in respective cylinders formed in a cylinder block and positioned circumferentially at a first radial distance about the rotational axis of a drive element. Many of these pump/motor machines have variable displacement capabilities, and they are generally of two basic designs. In the first basic design, the pistons reciprocate in a rotating cylinder block against a variably inclined, but otherwise fixed, swash plate. In the second basic design, the pistons reciprocate in a fixed cylinder block against a variably inclined and rotating swash plate that is often split to include a non-rotating, nutating-only “wobbler” that slides upon the surface of a rotating and nutating rotor. While the invention herein is applicable to both of these designs, it is particularly appropriate for, and is described herein as, an improvement in the latter type of machine in which the pistons reciprocate in a fixed cylinder block.
The pumps and motors utilized in the invention and described herein are liquid-type hydraulic machines and it should be understood that the terms fluid and pressurized fluid as used herein throughout, are intended to identify incompressible liquids rather than compressible gases. Because of the incompressibility of liquids, the pressure and load duty cycles of these two different types of hydraulic machines are so radically different that designs for the gas compression type machines are inappropriate for use in the liquid-type machines, and visa versa. Therefore, the following remarks should all be understood to be directed and applicable to liquid-type hydraulic machines and, primarily, to such heavy-duty automotive applications as those identified above.
Hydraulic machines with fixed cylinder blocks can be built much lighter and smaller than the machines that must support and protect heavy rotating cylinder blocks. However, these lighter machines require rotating and nutating swash plate assemblies that are difficult to mount and support. For high-pressure/high-speed service, the swash plate assembly must be supported in a manner that allows for the relative motion between the heads of the non-rotating pistons and a mating surface of the rotating and nutating swash plate. Such prior art swash plates have often been split into a rotating/nutating rotor portion and a nutating-only wobbler portion, the latter including pockets that mate with the heads of the non-rotating pistons through connecting “dog-bones”.
That is, such fixed-cylinder-block machines have heretofore used a “dog-bone” extension rod (i.e., a rod with two spherical ends) to interconnect one end of each piston with the surface of the nutating-but-not-rotating wobbler. One spherical end of the dog-bone is pivotally mounted into the head end of the piston, while the other spherical end is usually held at all times in a pocket of the swash plate wobbler during all relative motions between the heads of the non-rotating pistons and the pockets of the nutating swash plate. As is well known in the art, these relative motions follow varying non-circular paths that occur at all inclinations of the swash plate away from 0°. These dog-bones greatly increase the complexity and cost of building the rotating swash plates of these lighter machines.
Dog-bone rods are also sometimes used to interconnect one end of each piston with the inclined (but not rotating) swash plates of hydraulic machines with rotating cylinder blocks. However, more often this latter type of machine omits such dog-bones, using instead elongated pistons, each having a spherical head at one end (again, usually covered by a pivotally-mounted conventional shoe element) that effectively contacts the non-rotating flat surface of the swash plate. Such elongated pistons are designed so that a significant portion of the axial cylindrical body of each piston remains supported by the walls of its respective cylinder at all times during even the maximum stroke of the piston. This additional support for such elongated pistons is designed to assure minimal lateral displacement of each spherical piston head as it slides over the inclined-but-not-rotating swash plate when the pistons rotate with their cylinder block.
Generally, these elongated pistons are primarily lubricated by “blow-by”, i.e., that portion of the high pressure fluid that is forced between the walls of each cylinder and the outer circumference of each piston body as the reciprocating piston drives or is driven by high pressure fluid. Such blow-by provides good lubrication only if tolerances permit the flow of sufficient fluid between the walls of the cylinder and the long cylindrical body of the piston, and blow-by sufficient to assure good lubrication often negatively affects the volumetric efficiency of the pump or motor machine. For instance, a 10 cubic inch machine can use as much as 4 gallons of fluid per minute for blow-by. While smaller tolerances can often be used to reduce blow-by, the reduction of such tolerances is limited by the needs for adequate lubrication that increase with the size of the pressure and duty loads of the machine. Of course, such blow-by is accomplished by using fluid that would otherwise be used to drive or be driven by the pistons to accomplish work. Therefore, in the example just given above, the 4 gallons of fluid per minute used for blow-by lubrication, reduces the volumetric efficiency of the machine.
The invention disclosed below is directed to improving the volumetric efficiency of such elongated-piston machines while, at the same time, assuring appropriate lubrication of the pistons and simplification of the apparatus used to maintain contact between the pistons and the swash plate.